[Reasoning] Logical Connectives (if, unless, either or) for CSAT, CAT shortcuts formulas approach explained

Aptitude193 Comments

  1. Difference: Syllogism vs Logical connectives
  2. Standard format: logical connectives
  3. Logical connective: if then
  4. Logical connective: Only IF
  5. Logical Connective: UNLESS
  6. Logical connective: otherwise
  7. Logical connective: When, Whenever, every time
  8. Logical Connective: Either OR
  9. Demo Q: Only if: bored TV brother (CSAT 2012)
  10. Demo Q (If, then) Professor Headaches  (CAT’98)
  11. Demo Q: Either or: derailed/late train (CAT’97)

Difference: Syllogism vs Logical connectives

Syllogism (all cats are dog) is a common and routinely appearing topic in most of the aptitude exams (Bank PO, LIC, SSC etc). But Logical connectives is rare. However, in UPSC CSAT 2012 the topic was asked, therefore, you’ve to prepare it.

Syllogism

Logical connectives

Contains words like “all, none, some” etc. Can be classified into UP, UN,PP and PN. Already explained in previous articles.Contains words like “if, unless, only if, whenever” etc. can be classified into 1, ~1, 2, ~2 (we’ll see in this article)
Have to mugup more formulas, takes more time than logical connective questions.Less formulas and quicker than syllogism.
Question Statements:

  1. All cats are dogs
  2. some pigs are cats
  3. no dogs are bird

Conclusion choices:

  1. Some cats are dogs
  2. No birds are cats
  3. some pigs are birds
  4. Some pigs are not birds
Question statements:

  1. I watch TV only if I am bored
  2. I am never bored when I have my brother’s company.
  3. Whenever I go to the theatre I take my brother along.

Conclusion choices:

  1. If I am bored I watch TV
  2. If I am bored, I seek my brother’s company.
  3. If I am not with my brother, than i’ll watch TV.
  4. If I am not bored I do not watch TV.

Standard format: logical connectives

  • If, unless, only if, whenever, every time etc. are examples of Logical connectives.
  • Whenever you’re given a question statement, first rule is: question statement must be in the standard format.
  • The standard format is
  • ****some logical connective word *** simple statement#1, simple statement #2.
  • It means, the question statement must start with a logical connective word, otherwise exchange position. For example
Given question statementExchange position?
If you’re in the army, you’ve to wear uniform
  • no need because the simple statement containing “IF” is given in the beginning. This is already in the standard format.
You’ve to wear uniform, if you’re in the army
  • We need to exchange position because the part containing “IF” is not given in the beginning of this statement, given statement is not in standard format.
  • Therefore, Rewrite given statement as
  • If you’re in the army, you’ve to wear uniform.
You’ve to salute, whenever Commanding Officer comes in your cabin.
  • Need to exchange position. Because statement doesn’t start with the logical connective “whenever”.
  • Therefore rewrite the given statement as
  • Whenever CO comes in your cabin, you have to salute.

Now let’s derive valid inferences for various logical connectives.

Logical connective: if then

Consider these two simple statements

  1. You’re in army
  2. You’ve to wear uniform.

These are two simple statements. Now I’ll combine these two simple statements (#1 and #2) to form a complex statement.

  • If you’re in army(#1), you have to wear uniform.(#2)

What about its reverse?

  • You’ve wearing uniform (#2)—> that means you’re in the army.(#1)
  • But there is possibility, you’re in navy—-> you’ll still have to wear a uniform. It means,
  • if 1=>2, then 2=>1 is not always a valid inference.
  • Let’s list all such scenarios in a table.
Given statement:If you’re in army(#1), you have to wear uniform.(#2)
Inference?Valid / invalid?
  1. If #2, then #1
If you’ve to wear uniform, you’re in army.you’ve to wear uniform in navy, air force, BSF etc. so this inference is not always valid.
  1. If not #1, then not #2
if you’re not in army, you don’t have to wear uniform.you’ve to wear uniform in navy, air force, BSF etc. so this inference is not always valid.
  1. if not #2, then not #1
If you don’t have to wear uniform, you’re not in army.Always valid.
  • In the exam, you don’t have to think ^that much. Just mugup the following rule:
  • Given statement =“If #1 then #2”, in such situation the only valid inference is “if Not #2, then not #1”.
  • In other words, “if 1st happens then 2nd happens”, in such situation, the only valid inference is “if 2nd did not happen then 1st did not happen”.
  • Now I want to construct a short and sweet reference table for the logical connective problems. So I’ll use the symbol ~= negative.

~1=meaning NOT 1 ( or in other words, negative of #1)

GivenValid inference
If 1, then 2If not 2, then not 1
If 1=>2~2=>~1
  • In some books, material, sites, you’ll find these rules explained as using “P” and “Q” instead of 1 and 2.
  • But in our method, you first make sure the given (complex) statement starts with a logical connective (or you exchange position as explained earlier)
  • We denote the first simple sentence as #1 and second simple sentence as #2.
  • The reason for using 1 and 2= makes things less complicated and easier to mugup.

Logical connective: Only IF

  • In such scenario, you’ve to rephrase given statement into “if then” and then apply the logical connective rule for “if then”.
  • For example: given statement: he scores a century, only if the match is fixed.
  • The “standard format”= only if the match is fixed(1), he scores a century(2).
  • In case of “only if”, we further convert it into an “if” statement, by exchanging positions. That is
  • if he scores a century(#2), the match is fixed(#1).
  • Then apply the formula for “if then” and get valid inference.
  • Here we’ve “if 2=>1” as per our formula for “if then”, the valid inference will be ~1=>~2. Don’t confuse between 1 and 2. Because essentially the valid inference is “negative of end part => negative of starting part”.
  • Therefore “if 2=>1 then ~1=~2”
  • similarly “if 98=>97, then valid inference will be ~97=>~98”
  • Similarly “if p=>q, then valid inference will be ~q=>~p”,
  • similarly “if b=>a, then valid inference will be ~a=~b”) .
  • Update our table
Logical connectiveGiven statementValid inference using symbolValid inf. In words
IfIf 1=>2~2=>~1Negative of end part=> negative of start part
Only ifOnly if 1=>2~1=>~2Negative of start part=>negative of end part.

Logical Connective: UNLESS

  • Given statement: Unless you bribe the minister(#1), you will not get the 2G license.(#2)
  • Unless = if…..not.
  • So, I can re-write the given statement as
  • (new) Given statement: If you don’t bribe the minister(#1), you’ll not get the 2G license.(#2)

How to come up with a valid inference here?

#1You don’t bribe the minister
#2You’ll not get the 2G license.
  • For “if..then”, We’ve mugged up the rule:  1=>2 then only valid inference is ~2=>~1. (in other words, negative of end part => negative of starting part).
  • let’s construct the valid inference for this 2G minister.
  • we want ~2 => ~1
  • Negative of (2) => negative of (1)
  • Negative of (you’ll not get the 2G license)=>negative of (you don’t bribe the minister)
  • You’ll get the 2G license => you bribe the minister.
  • In other words, If I see a 2G license in your hand, then I can infer that you had definitely bribed the minister.
  • This is one way of doing “unless” questions = via converting it into “if…not” type of statement.
  • The short cut is to mugup another formula: unless1=>2 then ~2=>1.
  • How did we come up with above formula?

Deriving the formula for unless

  • Unless 1=>2 (given statement)
  • if not 1=>2  (because unless=if not)
  • if ~1=>2 (I’m using symbol ~ instead of “not”)
  • ~2=> ~(~1) (because we already mugged up the rule “if 1=>2, then valid inference is ~2=>~1)
  • ~2=>1 (because ~(~1) means double negative and double negative is positive hence ~(~1)=1)

This is our second rule: Unless1=>2 then ~2=>1

Table

Logical connectiveGiven statementValid inference using symbolValid inf. In words
IfIf 1=>2~2=>~1Negative of end part=> negative of start part
Only ifOnly if 1=>2~1=>~2Negative of start part=>negative of end part.
UnlessUnless 1=>2~2=>1Negative of end part=>start part unchanged.

Logical connective: otherwise

  • Suppose given statement is: 1, otherwise 2.
  • you can write it as unless 1 then 2.  (unless1=>2)
  • Then use the formula for “unless.”

Logical connective: When, Whenever, every time

  • Given statement: he scores century, when match is fixed.
  • This is not in standard format of “**logical connective word**, simple statement #1, simple statement #2.”
  • So first I need to exchange the positions: “when match is fixed (#1), he scores century (#2)”.
  • In case of when and whenever, the valid inference is= same like “If, then”. That means negative of end part=>negative of starting part.
  • Same formula works for “whenever” and “Everytime”.
  • Update the table
Logical connectiveGiven statementValid inference using symbolValid inf. In words
IfIf 1=>2~2=~1Negative of end part=> negative of starting part
WhenWhen 1=>2
WheneverWhenever 1=>2
EverytimeEverytime 1=>2
Only ifOnly if 1=>2~1=>~2Negative of start part=>negative of end part.
UnlessUnless 1=>2~2=>1Negative of end part=>starting part unchanged.

Logical Connective: Either OR

Given statement: Either he is drunk(1) or he is ill(2).

In such cases, if not 1 then 2. And if not 2 then 1.

Meaning,

  1. if he is not drunk then he is definitely ill
  2. if he is not ill, then he is definitely drunk

both are valid. Update the table

Logical connectiveGiven statementValid inference using symbolValid inf. In words
IfIf 1=>2~2=~1Negative of end part=> negative of starting part
WhenWhen 1=>2
WheneverWhenever 1=>2
EverytimeEverytime 1=>2
Only ifOnly if 1=>2~1=>~2Negative of start part=>negative of end part.
UnlessUnless 1=>2~2=>1Negative of end part=>starting part unchanged.
Otherwise1 otherwise 2=> rewrite as Unless1=>2.
Either orEither 1 or 2
  • ~2=>1
  • ~1=>2
Negative of any one part=> remaining part remains unchanged.
  • Now let’s solve some questions from old CSAT and CAT papers
  • Please note: in the exam, actual wording / meaning of the simple statement doesn’t matter. Just apply the formulas as given in above table.
  • For example, “if you’re in army, you have to wear uniform.” Then valid inference is ~2=>~1 (you don’t have to wear uniform, then you’re not in army).
  • Now ofcourse there would be exceptional situation when army officer/jawan doesn’t need to wear uniform, for example during espionage mission behind the enemy lines. In that case you don’t have to wear uniform, but you’re still in the army.
  • But keep in mind, while solving logical connective question under the “aptitude/reasoning” portion you don’t have to surgically dissect or nitpick the meaning every statement. Just “if 1=>2” then “~2=>~1”.

Demo Q: Only if: bored TV brother (CSAT 2012)

Examine the following statements:

  1. I watch TV only if I am bored
  2. I am never bored when I have my brother’s company.
  3. Whenever I go to the theatre I take my brother along.

Which one of the following conclusions is valid in the context of the above statements?

  1. If I am bored I watch TV
  2. If I am bored, I seek my brother’s company.
  3. If I am not with my brother, then I’ll watch TV.
  4. If I am not bored I do not watch TV.

Approach

First we’ll construct valid inferences from the question statements

Given Question Statement #1:

  • Given =I watch TV only if I am bored
  • This is not in standard format. So first exchange position
  • Only if I’m bored (1), I watch TV(2)
  • What is the valid inference? Just look at the formula table
  • Only if 1=>2 then ~1=~2
  • Valid inference= if I’m not bored, I do not watch TV.
  • Look at the statements given in the answer choices, (D) matches. Therefore, final answer is (D).

Demo Q (If, then) Professor Headaches  (CAT’98)

You’re given a statement, followed by four statements labeled A to D. Choose the ordered pair of statements where the first statement implies the second and two statements are logically consistent with the main statement.

Given statement: If I talk to my professors(1), then I didn’t need to take a pill for headache.(2)

Four Statements

  1. I talked to my professors
  2. I did not need to take a pill for headache
  3. I needed to take a pill for headache
  4. I did not talk to my professor.

Answer choices

  1. AB
  2. DC
  3. CD
  4. AB and CD

Approach

Given statement is in standard format already

#1I talk to my professors
#2I didn’t need to take a pill for headache.

Let’s classify the four statements

ClassificationFour statements
1
  1. I talked to my professors
2
  1. I did not need to take a pill for headache
~2
  1. I needed to take a pill for headache
~1
  1. I did not talk to my professor.

Answer choice (i) AB

If you observe the answer choice (I): AB= I talked to my professors, I did not need to take a pill for headache. This is valid because if 1=>2 is already given in the question statement itself.

Answer choice (ii) DC

  • I did not talk to my professor (~1), I needed to take a pill for headache (~2). Meaning ~1=>~2.
  • This is invalid because as per our table, if 1=>2, then valid inference is ~2=>~1.

Answer choice (iii) CD

I needed to take pill for headache (~2), I did not talk to my professor (~1). Meaning ~2=>~1. This is valid as per our table. Therefore final answer is (IV) AB and CD

Demo Q: Either or: derailed/late train (CAT’97)

Given statement: either the train is late (1) or it has derailed (2)

Four statements

  1. Train is late = 1
  2. Train is not late = ~1
  3. Train is derailed =2
  4. Train is not derailed =~2

(^note: I’ve classified the statements in advance)

Answer choice

  1. AB
  2. DB
  3. CA
  4. BC

Approach

As per our table, the valid inferences for either or are

~2=>1If the train is not derailed, it is late.DA
~1=>2If the train is not late, it is derailedBC

Correct answer is (III): BC
For more articles on reasoning and aptitude, visit Mrunal.org/aptitude

Mrunal recommends

  1. (free) NCERT, NIOS, TN-Books
  2. Environment by ShankarIAS
  3. Indian Polity M.Laxmikanth (Hindi | English)
  4. Art & Culture by Nitin Singhania (Hindi | English)
  5. Spectrum: Modern History (Hindi | English)
  6. Bipin Chandra: Post Independence
  7. Fast-track to Arithmetic Rajesh Verma
  8. MK Pandey’s Analytical Reasoning
  9. Disha’s Topicwise Paperset (Hindi | English)
  10. School Atlas
  11. Mains: Language papers
  1. (free) NCERT, NIOS, TN-Books 4 History,Geo,Sci
  2. Indian Polity M.Laxmikanth (Hindi | English)
  3. Spectrum: Modern History (Hindi | English)
  4. Maths: Quantam CAT Sarvesh Kumar
  5. Objective General English SP Bakshi
  6. Word Power made Easy -Norman Lowe
  7. Topic wise Solved Paperset by Disha


So far 193 Comments posted

  1. Vengatesh

    Sir thank you very much

  2. gaurav

    mrunal sir what wil we do if word DESPITE comes..plz reply

  3. CARM

    Thanks Mrunal
    in ur article….last line should be
    Correct Ans is IV BC
    Anyways
    Can u help me with this

    1)The aircraft takes off if the light blinks
    2)Only if there is no storm the aircraft takes off
    3)If there is a storm the light does blink

    options
    a. if the light blinks there is no storm
    b. the aircraft takes off if there is no storm

    Solution
    storm==>not take off===>not blink
    blink ===>no storm====>…….

    here cant we add “take off” which will make option b also true.(can see option a is true)
    if not why cant we do that
    Plz answer!!!!

    1. shani

      option A cannt be correct
      3)If there is a storm(1) the light does blink(2)
      n as per rules
      -(2)=>-(1) 0r (1)=>(2)
      and a. if the light blinks there is no storm
      this is contradictory

      1. neelima

        shani ji here both statements a & b are wrong na

        1. love shandilya

          yupp both r wrng

        2. Kritika

          Statement B is correct. It is rephrase of given statement “Only if there is no storm the aircraft takes off” -> The aircraft takes off (only) if there is no storm.

          1. Rahul

            A is wrong, right?

      2. shani

        what is wrong in option b??

    2. Rahul

      actually u tiped it wrong… 3)it must be “doesnt”
      if its not, then 1 and 3 contradicts each other.
      In that case option A is wrong and B is right.

  4. Aditya_S8

    sir post some practice questions too or refer to some book from where we may get some good questions 4 practice.

  5. freak

    First time i understand these thing in a very lucid manner…..thanks to u mrunal!!!!

    1. freak

      thanks u mrunal

  6. manoj

    thank you so much !! you are really a true teacher or much more then that….awesome explanation man !!

  7. ganesh gupta

    Sir u are great, u explain tough things with ease. I like all your articles. U are a great teacher. U are doing a great job, God has to bless u.

  8. help

    Dear Mrunal, how many months of study is necessary to clear upsc cse to become an IAS or IPS ? Thank you.

  9. Alok

    Hi Mrunal
    thanks a lot for all ur help
    Can u please give some explanation on type of Syllogism questions where we have to find which of statements are “both can be true but both cannot be false ” or ” both can be false but cannot be true” or ” both can be true and both can be false”
    Pls throw some light on this kind of questions , it was asked in 2011 paper

  10. Anurag

    Pl help me with following ques
    When ever shyam hears of an exam, he losses sleep
    a) shyam heard of an exam
    b) shyam didnt heard of an exam
    c) shyam lost slepp
    d) shyam didnt lost losse sleep
    Option —
    1) CA
    2) BD
    3) DB
    4) AD
    Ans according to TMH is – 1,

    1. shani

      CA cnnt be answer as per rules
      When ever shyam hears of an exam(1), he losses sleep(2)
      so as per rules
      -(2)=>-(1) OR (1)=>(2) n CA IS contradictory so it cnnt be

    2. amit

      ansr= DB ~2=>~1

    3. monu

      please apply ur mind… don’t blindly belief on any guide………… or material. answer is (DB)

  11. Anurag

    Another question

    when i see horror movie i had a bad dream
    a) i saw a horror movie
    b) i didnt saw a horroe movie
    c) i didnt had a bad dream
    d) i had a bad dream

    option :
    1) CB
    2)AD
    3) BC
    4) AC

    Answer According to TMH – a, but m confused b/w option 1 & 2

    1. shani

      yupp both r ryt

    2. amit

      ansr CB ~2=>~1 ,,v hv to mk inference. 2nd option is just qusn statemnt but if in ansr they gv both ,,,tick both oderws CB.

    3. zeenat samim

      restatement is never a valid answer, its neither a conclusion nor a reason.

  12. Gaurav

    @anurag……. option 3 in sleep wala ques.
    N both 1 n 2 are correct in bad dream ques.

    1. anurag

      Thanks Gaurav

  13. PRAKAH K S

    Hello Sir thanks a lot for simplifying sylloligism. Sir, Somewhere in ur blog u mentioned abt tool which remove unwanted texts before taking printout, so that it will save lot of pages. could you please mention abt tht tool so tht we can save no of pages and also money 🙂 while taking printout.

  14. j

    @parthi

    Basically if we make the venn diagram of both the options they would be same. I guess this seems like a bug with with venn diagram method. Well, but wat seems more appropraite is if rivers flows c cranks and not the other way round as see…
    If A then B cannot be stated as only if B then A when i guess their Venn diagrams would be identical. Let me know!

  15. SUMIT KARELI

    Thanks a lot….

  16. j

    Wat do we infer from ” all except a few” some are and simultaneously some are not?

  17. Amit

    Please help…
    1)some who study will not become graduates.
    2)To become graduates student must study.
    3) Only students can become graduates.

    conclusion:-
    a)Some who become graduates are not student.
    b)All students who study become graduates.
    c)Some who study and become graduates are students.
    d)Students who do not study will not graduate.

    1. मनु झा

      C & D can be concluded becuase the statement 2 says To become Graduates students MUST study. and 3rd says that only Students can become Graduates.
      In Mathematics-
      That means Graduate is a subset of Study and Student both and
      Study is a subset of Student.
      so there are 3 concentric circles with Student the outer most, then Study and the inneromst circle is Graduate.

      In simple words (i m trying)-
      A) Graduates are students first,grads second Why ? because state 3 says ONLY studs can become Grads. Hence this cant be concluded.
      B) All students who study cant be sure that they will DEF Graduate (just as 17lakh applicants gave SBI but only 1500 will be selected), anyways, because Statement1 says Some who study still not Graduate. Hence this cant be concluded.
      C) Since the 3rd statement says , that whosover is Grad he is a Student too and State 2 says that Stud must have studied to become Grad. Hence this can be concluded.
      D) Students who dont study = Can never Graduate. Why ? Because st2 says They MUST study but its not necessary that they will DEFINITELY graduate. but they stand a chance. Hence this can be concluded.

      I hope it helps. Do tell the Answer too.

      1. vikky

        Except “A” other conclusions r correct. 3 concentric circles ll not come. Please check. B can be concluded as second statement says “2)To become graduates student must study.”. so students if they study ll become graduate. (SBI s a competitive xam so all will not clear, but any student can become graduate provided he studies. NOTE :Even i am a graduate =D )..

        1. मनु झा

          Vikky

    2. HK

      i dont think C can be concluded because

      Only Students = Graduates (and no other)
      quantifier in C is “some” it has to be “ALL”
      Lets say i am doctor and i study
      if i become graduate i must have been Student. so not some but All

      ans is D

      ANSWER??

      1. मनु झा

        Your point is correct but here its not that Statement cant be concluded.

        Whenever its given –

        “All Roads are infrastructure.”

        Then you can always conclude that – “Some Roads are infrastructure.”
        Its not necessary that if ALL is given then the conclusion must have all. It can obviously have “SOME” .

        1. HK

          i disagree,

          All roads are infra. subject is distributed.. its not logically correct to blur the space boundary
          though true in common sense

          some roads are infra cant be “concluded” because in this statement neither subject nor object is distributed..

          as roads is Subset of infra we can say that some infra is roads. it not a conclusion too because its an INVERSE

          BHAI JISNE POOCHA HAI QUESTION WOH ANSWER TO BTA DOOOO…….

          1. k

            I think it is C and D both. And the explaination of manu jha is correct. pls correct answer?

  18. naina agarwal

    sir, in question..you can see the star only if you go to cinema…correct answer should be i didnt see the star i didn’t go to cinema..bt reverse is givn…please help me with this thnku…

    1. naina agarwal

      i got the solution..thnku..

  19. Tej Bharath

    You are the king,, mrunal…

  20. zeenat samim

    mrunal, can i infer from your explanation of “either – or” type-
    that answer format will be :-
    -1(negative of first part)and 2(unchanged second part)
    ?????

  21. pramod

    Sir, it is very interesting and very good elaboration. i read a book of CAT (author name started by a. not mentioning full name). but there i does not find the same thing as u wrote . thanks ………..

  22. anil bishnoi

    thanx for the explanation…it will be nice if u elaborate on more interconnected sentence for
    e.g If ankita eats pastry, then it is a black forest or a pineapple.

    plz xplain all the possible outcome.

  23. durga prasad

    hello Admin,
    I am new to this site. For the info above discussed there are other valid outcomes as well.
    Only if 1=> 2 it also mean 2=>1 apart from ~1=>~2. Please confirm it.

  24. Kulvinder ruhil

    Dear Mrunal Sir,
    Your methods to derive conclusions only in negatives like not 1 not 2 types .
    I faced a lot of problem while facing questions based on non negative conclusion.One more doubt Can I derive another conclusion based on two already derive conclusions.
    Q.1
    1.He writes whenever he is angry.
    2.It is cloudy only if he is angry.
    3.He is angry only if he is hungry.
    Conclusion
    A.He writes whenever he is hungry.
    B.He is hungry if he writes.
    C.He writes only if it is cloudy.
    D.Whenever it is cloudy,he writes.
    Q-2
    1.There are as many engineers in this organisation as there are doctors.
    2.Only if a doctor agrees to a plan will an engineer agree to plan.
    3.An engineer agrres to a plan only if the majority of engineers including him agree to it.
    Conclusions
    A.Only if an engineer agree to a plan will a doctor agree to it.
    B.An engineer will agree to plan if all doctor agree to it.
    C.An engineer might agree to a plan if the total number of engineers agreeing to a plan is more than half the total numbers of doctors.
    D.If all doctors agree to a plan,all engineers agree to it as well.

    Reply asap.

  25. Ravi Prasad

    Hello Sir
    although option D)If I am not bored I do not watch TV. (csat 2012)
    can definitely be concluded.
    why not option
    B)If I am bored, I seek my brother’s company.
    bcoz I am bored = negative of ( i am not bored) also
    I SEEK my brother company = does not SEEK here mean that HE IS NOT
    IN HIS BROTHER’S COMPANY.
    IF AM WRONG PLEASE CORRECT….

  26. priti

    i really appreciate ur contribution for us sir .every time i read ur article i just say -u r really too good and in my view best tr .

  27. aditi

    Hw can i Solve ths:::

    You cannot clear the CSAT unless you are intelligent
    1 u r intelligent
    2u can clear the CSAT
    3 u r nt intelligent
    4 u cannot clear the CSAT

    answer is :: C……….. How???? Plz help me!!

    1. nishat

      tell us all the options first.
      how do we know what is A , B, C and D?

      1. aditi

        thnx for reply…
        You cannot clear the CSAT unless you are intelligent
        a u r intelligent
        b u can clear the CSAT
        c u r nt intelligent
        d u cannot clear the CSAT

        conclusion: are bd, ac, cd, ab, ; given ans is cd, how? accordingly above, valid interference is ~2=>1, ~2 cancels negative sentence ; is m right????

        plz

        1. vips

          look…it means if u cleared the csat, u r intelligent….ie all csat are intelligent….draw a venn with intelligent encircling csat and u get ur answer…not intelligent means no csat,,,,

        2. PUSHKAR

          we can write it as
          you can clear CSAT only if you are intelligent
          means if you cleared CSAT then definitely you are intelligent but if you are intelligent you cannot say that you can definitely clear CSAT
          also if you are not intelligent then you cannot clear CSAT but it does not mean that if you have not cleared CSAT then you are not intelligent i.e. (you may be intelligent)

          1. PUSHKAR

            so answer is CD

    2. love shandilya

      luk aditi
      You cannot clear the CSAT unless you are intelligent
      U CAN WRITE DYS AS
      unless you are intelligent,You cannot clear the CSAT
      NOW ABOVE SENTENCE CAN BE WRITTEN IN D FRM LYK DAT
      UNLESS => IF…NOT
      so …….if you r nt intellignt ,u cannot clear CSAT
      NOW SIMPLY APPLY D LOGIC OF IF NOT
      2 SOLUTIONS R POSSIBLE
      RULE A…~2=~1
      RULE B…1=2
      SO WE WILL;TOOK CD as a answer by applyn RULE B
      on d other syd other options not CRRCT
      HOPE U UNDRSTND D SOLUTION

  28. subramaniyan

    Dear sir,
    Whether in the last example ,AD and DA are both possible. Please enlighten us 🙂

  29. amal

    damn good man..

  30. sunny verma

    Sir,
    How to solve a question which do not contain any “if” and “only if”. Below is the question asked in CL test series:

    Statement: There are as many engineer in the organization as there are doctors.

  31. sunny verma

    another question which i am unable to solve is following:

    statements are:
    1. whenever prices goes up , farmers are affected
    2. Farmers are affected only if it does not rain
    3. It rains if there are clouds
    Which of the following conclusion can be drawn:
    a) Farmers are always affected by rains,
    b) If it does not rain Farmers are affected
    c) Whenever there are clouds prices go up
    d) If there are clouds farmers are not affected

    Correct Answer is D, But how and how to solve option A?

  32. RKS

    1) Prices up —-> Farmers affected (FA)
    2) NO rain —–> FA
    3) Clouds —-> Rains

    So,
    OP 1) Does not qualify as —- FA by Price rise also
    OP 2) Does not qualify as —- FA by Price rise also
    OP 3) No relation between the three
    OP 4) Correct – coz CLOUDS —-> Rains —-> Farmers NOT affected.

    Hope this helps.

    thanks

    1. sunny verma

      Thanks for your reply but kindly explains below related queries:
      1. as per universal rule.. only if p then q : q->p && ~p->~q so deduction of statement 2 [“Farmers are affected only if it does not rain”] would be as follows
      FA -> No rain && Rain->no FA

      but you have derived it as ” 2) NO rain —–> FA “… HOW??

  33. vips

    pretty easy mate…… u can solve simply by logic… statement 2 is antithema of conclusion 1,,,
    more systematic approach…1. price imples farmers affection ie all prices are farmers… 2 //farmers implies no rain…3 cloud imples rain that all cloud are rain…
    now draw venn with prices encircled by farmers in turn encircled by no rain and separate circle of cloud u get ur answer

  34. vips

    ask any csat question… can ask gs as well

  35. dark funtazy

    question -if P runs for president, C does not.
    answers 1.P runs for president,C does not.
    2.C runs for president,P does not.
    3.both P and C run for president.
    4.neither P nor C run for president.
    which of the above 4 statements are correct.

  36. dark funtazy

    question -if P runs for president, C does not.
    answers 1.P runs for president,C does not.
    2.C runs for president,P does not.
    3.both P and C run for president.
    4.neither P nor C run for president.
    which of the above 4 statements are correct.

  37. PRAVEEN

    SUPERB EXPLAINATION……. YET NEED OF SOME MORE EXAMPLES TO SOLVE N PRACTICE SR

  38. Shibprasad

    for Unless, is it ~ 2=> 1 or ~2=>~1 , please clarify

  39. Shibprasad

    sorry got it, thanks

  40. sumit

    hi sir want to prepare for the post of probationary officer and rbi grade b officer so please suggest me the best practise paper and also economics and banking terms…its my humble request to u and thanking you

  41. chandan ongole

    Sir,
    kindly elaborate the negation of a statement…

  42. Subhajit Dasgupta

    Directions:- Each question below consists of a main statement followed by four numbered statements. From the numbered statements, select the one that logically follows the main statement.

    q1> Unless Sangeeta’s boss sanctions her leave and books the tickets, Sangeeta cannot go home for diwali.

    a>Sangeeta is going home for diwali, hence, her boss booked her tickets but did not sanction leave.
    b>Sangeeta is going home for dipawali,implies that her boss sanctioned leave but the tickets are not booked.
    c>Sangeeta’s ticket was not booked implies, she is not going home for diwali.
    d>More than one of the above.

    Can you please explain me these type of questions with this example and if possible some other examples too??

  43. shamsher

    Is it necessary to take coaching for REASONING IN CSAT?

  44. Nimisha Srivastava

    Why are 1=> ~2 and 2=>~1 incorrect inferences in “Either/Or” questions? If one happens, the other doesn’t, since it is ‘either this, or that’ right? I am not able to understand the logic behind why it is incorrect. Someone please help if possible!

    1. Praveen_R

      In either/or any one condition need to be fulfilled for the desired outcome. If cond. 1 is false, then cond-2 needs to be true and vice versa.
      Either RaGa will be PM or Namo.

      Not Raga->Namo
      Not Namo -> Raga

  45. mani

    nice article on logical deduction very easy to understand via this article.. thanku sir.:)

  46. Karan patil

    Mrunal u rock bro . Lovely article

  47. DBM

    Thanks a lot, Mrunal. This is what I needed! So clearly explained.

  48. Ankush rana

    Can you help me on this…
    Q-whenever pollution is on the rise,vehicles will be stopped and their emission level eill be checked.
    A)vehicles are not stopped or their emission level are not checked, means that the pollution is not on the rise.
    B)if vehicles are not stopped but i pollution is on the rise,then emission levelslevel of vehiclesfear will definitelybe be checked.
    C)if vehicles are stopped and their emission levels are not checked, it means that the pollution is not on rise.
    D)both a and c
    E)both b and a

    Answer-D bith a and c
    explain why

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